Non-volatile memory apparatus and methods

ABSTRACT

Some embodiments include apparatus and methods having memory cells coupled in series and a module to cause an application of voltages with at least three different values to gates of the memory cells during an operation to retrieve information stored in at least one of the memory cells. Additional apparatus and methods are described.

BACKGROUND

Non-volatile memory devices, such as flash memory devices, are used inmany computers and other electronic products to store information. Aflash memory device stores information in numerous memory cells, whichare usually formed in a semiconductor chip. Each of the memory cellsoften has a metal-oxide semiconductor (MOS) transistor with twodifferent transistor gates: a control gate and a so-called “floating”gate. The control gate is used to turn the transistor on and off tocontrol access to the memory cell. The floating gate is usually a placewhere information is stored in each memory cell.

A flash memory device usually has a programming operation to storeinformation into the memory cells, a read operation to retrieveinformation from the memory cells, and an erase operation to clearinformation from the memory cells. Programming, read, and eraseoperations usually involve applying voltages to the control gates of thememory cells and to other device components within the flash memorydevice. A conventional flash memory device often goes through manyprogramming, read, and erase operations during its life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a memory device, according to an exampleembodiment of the invention.

FIG. 2 shows a partial schematic diagram of a memory device, accordingto an example embodiment of the invention.

FIG. 3 shows a diagram of a partial cross-section of the memory deviceof FIG. 2, according to an example embodiment of the invention.

FIG. 4 shows a diagram of a portion of a memory device with voltagesapplied to gates of memory cells of the memory device during a readoperation, according to an example embodiment of the invention.

FIG. 5 shows a diagram of a portion of a memory device with threevoltages applied to gates of different selected memory cells atdifferent read operations of the memory device, according to an exampleembodiment of the invention.

FIG. 6 shows a diagram of a portion of a memory device with fourvoltages applied to gates of different selected memory cells atdifferent read operations, according to an example embodiment of theinvention.

FIG. 7 is a flow chart showing a method, according to an exampleembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a memory device 100, according to anexample embodiment of the invention. Memory device 100 includes a memoryarray 102 with memory cells 104 arranged in rows and columns. Rowdecoder 106 and column decoder 108 respond to an address register 112and selectively access memory cells 104 based on row address and columnaddress signals on lines 110. A data input/output circuit 114 maytransfer information (e.g., data) between memory cells 104 and lines110. A sense unit, such as sense amplifier unit 103, operates to sensesignals associated with selected memory cells during a memory operationto determine information stored in the selected memory cells. A controlcircuit 116 controls operations of memory device 100 based on signals onlines 110 and 111. Memory device 100 can be a flash memory device; theflash memory device can include a NAND flash memory device where memorycells 104 includes flash memory cells arranged in a NAND flash memoryarrangement. One skilled in the art will readily recognize that memorydevice 100 includes other parts, which are omitted from FIG. 1 to focuson the various embodiments described herein.

Memory device 100 includes lines 130 and 132 to receive voltages Vcc andVss. Voltage Vcc can be a supply voltage for memory device 100. VoltageVss can be a reference voltage, such as a ground potential. Memorydevice 100 also includes a voltage generator 140. Voltage generator 140and control circuit 116 (or parts thereof) may act separately ortogether to cause different voltage values to be applied to memory array102, such as by providing the different voltages to the memory array102. Accordingly, voltage generator 140 and control circuit 116 (orparts thereof) may be referred to separately or together as a module tocause the application of different voltage values. The operationsinclude a programming operation to store information into memory cells104, a read operation to retrieve information from memory cells 104, andan erase operation to clear information from all or a portion of memorycells 104. Memory device 100 includes the memory devices and theirassociated operations described below with reference to FIG. 2 thoughFIG. 7.

FIG. 2 shows a partial schematic diagram of a memory device 200,according to an example embodiment of the invention. Memory device 200includes a number of memory cells 210, 211, 212, 213, 214, 215, 216, and217 arranged in rows 220, 221, 222, 223, 224, 225, 226, and 227 andcolumns 230, 231, and 232. Each of the memory cells includes a floatinggate 208 and a control gate 209. The memory cells in the same column areconnected in series to form a string of memory cells, such as strings240, 241, and 242. Memory device 200 includes lines (e.g., access lines,such as word lines) 250, 251, 252, 253, 254, 255, 256, and 257associated with the rows. Memory device 200 also includes lines (e.g.,sense lines, such as bit lines) 260, 261, and 262 associated with thecolumns. Control gates 209 of memory cells in the same row (row 220through 227) are coupled to the same line (one of lines 250 through 257)associated with that row. FIG. 2 shows an example of three strings witheight memory cells in each string. The number of strings and the numbermemory cells in each string may vary.

Memory device 200 includes select transistors 271, each being coupledbetween one of strings 240, 241, and 242 and a source line 270, whichhas a signal SL. Each select transistor 271 includes a gate 272 coupledto a select line 273. A select signal SGS on select line 273 can be usedto activate (turn on) select transistors 271 to electrically couplestrings 240, 241, and 242 to line 270 during a memory operation (e.g., aread operation). Memory device 200 also includes select transistors 281,each being coupled between one of strings 240, 241, and 242 and one oflines 260, 261, and 262; these lines have corresponding signals BL0,BL1, and BL2. Each select transistor 281 includes a gate 282 coupled toa select line 283. A select signal SGD on select line 283 can be used toactivate select transistors 281 to electrically couple strings 240, 241,and 242 to lines 260, 261, and 262 during a memory operation (e.g., aread operation).

In memory device 200, to program, read, or erase the memory, appropriatevoltages can be applied to a combination of: select lines 273 and 283;lines 250 through lines 257; lines 260, 261, and 262; and source line270. To focus on the embodiments herein, this description omits thediscussion related to programming and erase operations.

As shown in FIG. 2, memory device 200 includes a voltage control circuit290, which can be a part of a control circuit and voltage generator ofmemory device 200 that are similar to control circuit 116 and voltagegenerator 140 of FIG. 1. In FIG. 2, in a read operation, voltage controlcircuit 290 applies voltages of different values to lines 250 throughlines 257 to retrieve information from a selected memory cell in one ormore of the strings 240, 241, and 242.

In the description herein, a selected memory cell refers to the memorycell that is selected during that particular read operation so thatinformation can be retrieved from it; unselected memory cells duringthat particular read operation refer to the memory cells that are notselected to retrieve information from them during that particular readoperation.

FIG. 3 shows a diagram of a partial cross-section of memory device 200of FIG. 2. FIG. 3 shows a partial cross-section of string 240 of memorydevice 200. Other strings (e.g., strings 241 and 242 in FIG. 2) havestructures similar or identical to the structure shown in FIG. 3. Asshown in FIG. 3, memory device 200 includes a substrate 301. In eachmemory cell 210 through 217, floating gate 208 and control gate 209 areformed above source/drain regions 360 of substrate 301 and are isolatedfrom each other by an insulating material 311. Each region 360 forms asource region (or drain region) of a transistor or forms a combinationof a source/drain region shared by two transistors, as shown in FIG. 3.

The following description of a read operation of memory device 200assumes memory cell 213 of string 240 is the selected memory cell; othermemory cells of string 240 are unselected memory cells.

In a read operation, memory device 200 turns on transistors 271 and 281to electrically couple string 240 to lines 260 and 270. A senseamplifier unit of memory device 200 (not shown in FIG. 2 and FIG. 3 butsimilar to sense amplifier unit 103 of FIG. 1) senses the value ofsignal BL0 on line 260 to determine the value of information in memorycell 213. The value (e.g., current or voltage value) of signal BL0 online 260 depends on whether a conductive path is formed between lines260 and 270. The conductive path is formed if the transistors in allmemory cells within the string 240 are turned on. A conductive path isnot formed if the transistor of the selected memory cell is not turnedon.

In the read operation, memory device 200 applies voltages V1, V2, and V3to gates 209 of memory cells 210 through 217. Voltages V1, V2, and V3have different values. As shown in FIG. 3, memory device 200 appliesvoltage V1 to gate 209 of (selected) memory cell 213, voltage V3 togates 209 of (unselected) memory cells 212 and 214 that are immediatelyadjacent memory cell 213, and voltage V2 to gates 209 of otherunselected memory cells of string 240. Voltages V2 and V3 havesufficient values that turn on transistors of unselected memory cells210, 211, and 212, regardless of the values of information stored inthese unselected memory cells, thereby forming a conductive segmentbetween line 270 and channels 363 and regions 360 of memory cells 210,211, and 212. Voltages V2 and V3 also have sufficient values that turnon transistors of unselected memory cells 214, 215, 216, and 217,regardless of the values of information stored in these unselectedmemory cells, thereby forming a conductive segment between line 260 andchannels 363 and regions 360 of memory cells 214, 215, 216, and 217. Aconductive path between lines 260 and 270 is formed if the transistor ofselected memory cell 213 is turned on, thereby forming a conductivesegment between channel 363 and regions 360 of memory cell 213

Voltage V1 has a value such that a conductive segment between channel363 and regions 360 of memory cell 213 is formed if memory cell 213 hasa threshold voltage value (e.g., a negative value) less than the valueof voltage V1. For example, the threshold voltage value of memory cell213 is less than the value of voltage V1 when memory cell 213 is not ina programmed state (e.g., when it is erased). The conductive segmentbetween channel 363 and regions 360 of memory cell 213 is not formed ifmemory cell 213 has a threshold voltage value (e.g., a positive value)greater than the value of voltage V1. For example, in what the industryrefers to as a single-level cell, the threshold voltage value of memorycell 213 is greater than the value of voltage V1 when memory cell 213 isin a programmed state (e.g., when it is not erased).

During a read operation, the value of information in memory cell 213 canbe determined based on current between lines 260 and 270. For example,current between lines 260 and 270 can be substantially zero if theconductive path between lines 260 and 270 is not formed and can be somepositive value if the conductive path between lines 260 and 270 isformed. Based on this current, memory device 200 appropriately providesan output signal to reflect the value of the information stored inmemory cell 213. Memory device 200 can provide the output signal tolines similar to lines 110 of FIG. 1.

As mentioned above, voltages V1, V2, and V3 have different values.Voltage V1 can have a value of zero volts. Voltage V3 can be greaterthan each of voltages V2 and V1. As shown in FIG. 3, V3=V2+X, where X isa positive voltage value. For example, voltage V2 can be approximately 5volts and X can be approximately 600 milivolts. Other values can beused.

In a memory device, such as memory device 200 of FIG. 3, impropercontrol of the voltages applied to the memory cells during a memoryoperation (e.g., a read operation) may lead to inferior deviceperformance, reduced device reliability, or both.

In memory device 200, the difference in values between voltages V2 andV3 can improve read operations, as explained in the flowing description.Voltages V2 and V3 applied at gates 209 creates an effective voltage ongates 208 of memory cells 210, 211, 212, 214, 215, 216, and 217 to turnon the transistors of these memory cells to create potential conductivesegments between lines 260 and 270, depending on the threshold voltagevalue memory cell 213, as described above. Since memory cells 212 and214 are immediately adjacent selected memory cell 213, if the samevoltage V2 is applied to gates 209 of all unselected memory cells, thenthe effective voltage on gates 208 of memory cells 212 and 214 can belower than the effective voltage on gates 208 of other memory cells(210, 211, 215, 216, and 217) that are farther from selected memory cell213 than each of memory cells 212 and 214. The reason of a lowereffective voltage on gates 208 of memory cells 212 and 214 is thatvoltage V1 at gate 209 of memory cell 213 has a value less than that ofvoltage V2 of adjacent memory cells 212 and 214 if voltage V2 is appliedto gates 209 of memory cells 212 and 214. The lower effective voltage ongates 208 of memory cells 212 and 214 may not efficiently turn on thetransistors of memory cells 212 and 214. Thus, current flowing on theconductive path (if it is formed) between lines 260 and 270 may beaffected (e.g. flowing less efficiently). This may make sensing currentduring the read operation less efficiently.

In memory device 200, since a voltage V3 having a value greater thanthat of voltage V2 is applied to gates 209 of memory cells 212 and 214,the effective voltage on gates 208 of memory cells 212 and 214 can beincreased to compensate for any potential reduction in their valuesbecause the difference in values between voltages V3 and V1 is greaterthan the difference in values between voltages V2 and V1. Thus, a moreuniform voltage on gates 208 of unselected memory cells can be obtained,and transistors of memory cells 212 and 214 can be turned on moreefficiently. This can improve the read operations in memory device 200.

In some cases, if voltage V2 is applied to gates 209 of all unselectedmemory cells, then the effective voltage on gate 208 of each of adjacentunselected memory cells 212 and 214 can be approximately ten percentless than the effective voltage on gates 208 of unselected memory cells210, 211, 215, 216, and 217. Thus, in some cases, selecting voltage V3with a value of approximately ten percent greater than the value ofvoltage V2 can compensate a potential reduction in effective voltage ongates 208 of adjacent unselected memory cells 212 and 214. Therefore, inthe equation V3=V2+X, the value of X can be selected such that theeffective voltage on gates 208 of memory cells 212 and 214 can beapproximately equal to the effective voltage on gates 208 of the otherunselected memory cells. For example, X can have a value such that thevalue of V3 is approximately ten percent greater than the value ofvoltage V2.

FIG. 4 shows a diagram of a portion of a memory device 400 with voltagesV1, V4, V5, and V6 applied to gates of memory cells 410 through 417during a read operation, according to an example embodiment of theinvention. Memory device 400 includes components similar to those ofmemory device 200 of FIG. 2 and FIG. 3. Similar components between FIG.3 and FIG. 4 have the same designation numbers. For simplicity, thedescription for the similar components between FIG. 3 and FIG. 4 is notrepeated.

As shown in FIG. 4, memory cell 413 is assumed to be a selected memorycell during a read operation of memory device 400; other memory cells410, 411, 412, 414, 415, 416, and 417 are unselected memory cells. Themain difference between the voltages V1, V4, V5, and V6 and voltages V1,V2 and V3, of FIG. 3 is that, in FIG. 4, four voltages V1, V4, V5, andV6 have different values applied to gates 409 of memory cells 410through 417. In FIG. 3, only three voltages V1, V2, and V3 havingdifferent values are applied to gates 209 of memory cells 210 through217.

As shown in FIG. 4, V6=V5+Y and V4=V5−Z, where Y and Z are positivevoltage values. Voltage V1 can be zero volts. Voltage V6 can correspondto voltage V3 of FIG. 3, and the value of Y can correspond to the valueof X in FIG. 3. The value of Z is less than the value of Y. In equationsV6=V5+Y and V4=V5−Z, the values of Y and Z can be selected such that theeffective voltage one gates 208 of memory cells 412 and 414 can beapproximately equal to the effective voltage on gates 208 of the otherunselected memory cells. For example, when voltage V1 is zero volts andvoltage V5 is approximately 5 volts, Y can be approximately 600milivolts, and Z can be approximately 200 milivolts.

In FIG. 4, since the value of voltage V6 is greater than the value ofvoltage V5, if voltage V5 is also applied to gates 209 of unselectedmemory cells 411 and 415, then the effective voltage on gates 208 ofmemory cells 411 and 415 can be different from (e.g., higher than) theeffective voltage on gates 208 of other unselected memory cells 210,216, and 217. Therefore, by applying voltage V4 that is less thanvoltage V5 to gates 209 of memory cells 411 and 415, the effectivevoltage on gates 208 of memory cells 411 and 415 can be alsosubstantially equal to the effective voltage on gates 208 of otherunselected memory cells, thereby further improving read operations inmemory device 400.

FIG. 5 shows a diagram of a portion of a memory device 500 with voltagesV1, Va, and Vb applied to gates of different selected memory cells atdifferent read operations 501, 502, 503, 504, and 505, according to anexample embodiment of the invention. Voltage Vsel, Va, and Vb canrespectively correspond to voltages V1, V2, and V3 of FIG. 3. Memorydevice 500 includes components similar to those of memory device 200 ofFIG. 2 and FIG. 3. Similar components between FIG. 3 and FIG. 5 have thesame designation numbers. For simplicity, the description for thesimilar components between FIG. 3 and FIG. 5 is not repeated.

In FIG. 5, in each of read operations 501, 502, 503, 504, and 505, theselected memory cell is the memory cell having Vsel applied to its gate209 (e.g., control gate). For example, in read operation 501, theselected memory cell is memory cell 510 having voltage Vsel applied toits gate 209, and the unselected memory cells are memory cells 511, 512,513, 514, 515, 516, and 517 having voltage Va or Vb applied to theirgates 209. Voltage Vb is greater than each of voltages Va and Vsel.Voltage Va is greater than voltage Vsel. Applying voltages Vsel, Va, andVb as shown in FIG. 5 during different read operations of memory device500 can have characteristics similar to those of memory device 200during a read operation, described above with reference to FIG. 2 andFIG. 3.

FIG. 6 shows a diagram of a portion of a memory device 600 with voltagesVsel, Vc, Vd, and Ve applied to gates of different selected memory cellsat different read operations 601, 602, 603, 604, and 605, according toan example embodiment of the invention. Voltage Vsel, Vc, Vd, and Ve canrespectively correspond to voltages V1, V4, V5, and V6 of FIG. 3. Memorydevice 600 includes components similar to those of memory device 200 ofFIG. 2 and FIG. 3. Thus, for simplicity, description for the similarcomponents between FIG. 3 and FIG. 6 (shown by the same designationnumbers) is not repeated.

In FIG. 6, in each of read operations 601, 602, 603, 604, and 605, theselected memory cell is the memory cell having Vsel applied to its gate209 (e.g., control gate). For example, in read operation 601, theselected memory cell is memory cell 610 having voltage Vsel applied toits gate 209, and the unselected memory cells are memory cells 611, 612,613, 614, 615, 616, and 617 having voltages Vc, Vd, or Ve applied totheir gates 209. Voltage Ve is greater than each of voltages Vc, Vd, andVsel. Voltage Vd is greater than voltage Vc. Voltage Vc is greater thanvoltage Vsel. Applying voltages Vsel, Vc, Vd, and Ve as shown in FIG. 6during different read operations of memory device 600 can havecharacteristics similar to those of memory device 200 and 400 during aread operation, described above with reference to FIG. 2, FIG. 3, andFIG. 4.

FIG. 7 is a flow chart showing a method 700 according to an exampleembodiment of the invention. Method 700 can be used in a memory device,such as memory device 100, 200, 400, 500, and 600 described above withreference to FIG. 1 through FIG. 6. In FIG. 7, activity 710 includesreceiving a command to retrieve information from at least one memorycell of the memory device. The command can be provided from anadditional device to lines of the memory device; the lines can besimilar to lines 110 and 111 of memory device 100 of FIG. 1. Theadditional device can be a processor, a memory controller, or otherdevices. Activity 720 in FIG. 7 includes applying voltages to the gates(e.g., control gates) of memory cells of the memory device. The voltagescan have at least three different values applied to the gates ofdifferent memory cells. Activity 730 includes providing information fromat least one selected memory cell to lines of the memory device afterinformation is retrieved from the selected memory cell. Activity 730 inFIG. 7 can includes providing the information to lines, similar to lines110 of FIG. 1. Method 700 can include additional activities similar tothose performed by memory device 100, 200, 400, 500, and 600 during aread operation described above with reference to FIG. 1 through FIG. 6.

One or more embodiments described herein include apparatus and methodshaving memory cells coupled in series and a module to cause applicationof voltages with at least three different values to gates of the memorycells during an operation to retrieve information stored in at least oneof the memory cells. Other embodiments, including additional apparatusand methods described above with reference to FIG. 1 through FIG. 7.

The illustrations of apparatus such as memory devices 100 and 200 areintended to provide a general understanding of the structure of variousembodiments and not a complete description of all the elements andfeatures of the apparatus that might make use of the structuresdescribed herein.

Any of the components described above with reference to FIG. 1 throughFIG. 7 can be implemented in a number of ways, including simulation viasoftware. Thus, apparatus (e.g., memory devices 100, 200, 400, 500, and600 including their associated circuit components) described above mayall be characterized as “modules” (or “module”) herein. Such modules mayinclude hardware circuitry, single and/or multi-processor circuits,memory circuits, software program modules and objects and/or firmware,and combinations thereof, as desired by the architect of the apparatus(e.g., memory devices 100, 200, 400, 500, and 600) or as appropriate forparticular implementations of various embodiments. For example, suchmodules may be included in a system operation simulation package, suchas a software electrical signal simulation package, a power usage anddistribution simulation package, a capacitance-inductance simulationpackage, a power/heat dissipation simulation package, a signaltransmission-reception simulation package, and/or a combination ofsoftware and hardware used to operate or simulate the operation ofvarious potential embodiments.

The apparatus of various embodiments includes or can be included inelectronic circuitry used in high-speed computers, communication andsignal processing circuitry, memory modules, portable memory storagedevices (e.g., thumb drives), single or multi-processor modules, singleor multiple embedded processors, multi-core processors, data switches,and application-specific modules including multilayer, multi-chipmodules. Such apparatus may further be included as sub-components withina variety of electronic systems, such as televisions, memory cellulartelephones, personal computers (e.g., laptop computers, desktopcomputers, handheld computers, tablet computers, etc.), workstations,radios, video players, audio players (e.g., MP3 (Motion Picture ExpertsGroup, Audio Layer 3) players), vehicles, medical devices (e.g., heartmonitor, blood pressure monitor, etc.), set top boxes, and others.

The above description and the drawings illustrate some embodiments ofthe invention to enable those skilled in the art to practice theembodiments of the invention. Other embodiments may incorporatestructural, logical, electrical, process, and other changes. In thedrawings, like features or like numerals describe substantially similarfeatures throughout the several views. Portions and features of someembodiments may be included in, or substituted for, those of others.Other embodiments will be apparent to those of skill in the art uponreading and understanding the above description.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) requiring anabstract that will allow the reader to quickly ascertain the nature andgist of the technical disclosure. The Abstract is submitted with theunderstanding that it will not be used to interpret or limit the claims.

1. An apparatus comprising: memory cells coupled in a series, each ofthe memory cells including a gate, the gates being electrically isolatedfrom each other; and a module to cause an application of voltages withat least three different values to gates of the memory cells during anoperation to retrieve information stored in a selected memory cell ofthe memory cells.
 2. The apparatus of claim 1 further comprising: linescoupled to the memory cells; and a sense amplifier unit coupled to thelines to sense signals on at least one of the lines during the operationto determine information stored in the selected memory cell.
 3. Theapparatus of claim 1, wherein the memory cells include a first memorycell immediately adjacent a first side of the selected memory cell and asecond memory cell immediately adjacent a second side of the selectedmemory cell, and wherein the module is to apply the voltages such that avoltage applied to the gate of each of the first and second memory cellsis greater than a voltage applied to the gates of other memory cells inthe series.
 4. The apparatus of claim 3, wherein the module includes acircuit to apply a first voltage included in the voltages to a gate of afirst memory cell of the memory cells and to apply a second voltageincluded in the voltages to a gate of a second memory cell of the memorycells, such that the first voltage has a value approximately ten percentgreater than a value of the second voltage.
 5. An apparatus comprising:a first memory cell including a first gate, a second memory cellincluding a second gate, and a third memory cell including a third gate,the first, second, and third memory cells coupled in series; and amodule to cause a selective application of a first voltage having afirst value to the first gate during an operation to retrieveinformation stored in the first memory cell, a second voltage having asecond value to the second gate during the operation, and a thirdvoltage having a third value to the third gate during the operation,wherein the first value is different from the second value and thesecond value is different from the third value.
 6. The apparatus ofclaim 5 further comprising: a fourth memory cell coupled in series withthe first, second, and third memory cells, the fourth memory cell andincluding a fourth gate, wherein the module is further to cause anapplication of a fourth voltage having a fourth value to the fourth gateduring the operation, and wherein the fourth value is equal to the thirdvalue.
 7. The apparatus of claim 6, wherein the first value includes areference voltage.
 8. An apparatus comprising: a first memory cellincluding a first gate, a second memory cell including a second gate, athird memory cell including a third gate, and a fourth memory cellincluding a fourth gate, the first, second, third, and fourth memorycells coupled in series, the second memory located between the first andthird memory cells, the third memory located between the second andfourth memory cells; and a module to cause a selective application afirst voltage having a first value to the first gate during an operationto retrieve information stored in the first memory cell, a secondvoltage having a second value greater than the first value to the secondgate during the memory operation, a third voltage having a third valueless than the second value to the third gate during the memoryoperation, and a fourth voltage having a fourth value different from thethird value to the fourth gate during the memory operation.
 9. Theapparatus of claim 8, wherein the fourth value is greater than the thirdvalue.
 10. The apparatus of claim 8, wherein the second value isapproximately 600 millivolts greater than the fourth value, and thefourth value is approximately 200 millivolts greater than the thirdvalue.
 11. The apparatus of claim 10, wherein the first value is aground potential.
 12. An apparatus comprising: a first memory cellincluding a gate to receive a first voltage having a first value duringa during an operation to retrieve information stored in the first memorycell; second memory cells coupled in series with the first memory celland located on a first side of the first memory cell, each of the secondmemory cells including a second gate, wherein at least two of the secondgates receive second voltages having different values during theoperation; and third memory cells coupled in series with the firstmemory cell and located on a second side opposite from the first side ofthe first memory cell, each of the third memory cells including a thirdgate, wherein at least two of the third gates receive third voltageshave different values during the operation.
 13. The apparatus of claim12, wherein the second memory cells include a first unselected memorycell immediately adjacent the first memory cell, and the third memorycells include a second unselected memory cell immediately adjacent thefirst memory cell, and wherein the second voltage applied to the secondgate of the second unselected memory cell is equal to the third voltageapplied to the third gate of the third unselected memory cell.
 14. Theapparatus of claim 13, wherein the second memory cells include a thirdunselected memory cell, and the second voltage applied to the secondgate of the third unselected memory cell is less than the second voltageapplied to the second gate of the second unselected memory cell.
 15. Amethod comprising: receiving a command to read information stored in atleast one of memory cells of a device during an operation of the device,the memory cells coupled in series, each of the memory cells including agate, the gates of the memory cells being electrically isolated fromeach other; and applying voltages having at least three different valuesto different gates during the operation.
 16. The method of claim 15further comprising: during the operation, sensing signals on linescoupled to a selected memory cell among the memory cells to determineinformation stored in the selected memory cell.
 17. The method of claim16, wherein applying the voltages include: applying a first voltage ofthe voltages to a first gate of a first memory cell of the memory cells;and applying a second voltage of the voltages to a second gate of asecond memory cell of the memory cells, wherein the first voltage has avalue approximately ten percent greater than a value of the secondvoltage.
 18. A method comprising: applying a first voltage having afirst value to a first gate of a first memory cell of a device during aread operation of the device; applying a second voltage having a secondvalue to a second gate of a second memory cell of the device during theread operation; and applying a third voltage having a third value to athird gate of a third memory cell of the device during the readoperation, the first, second, and third memory cells coupled in series,wherein the third value is greater than the second value and the secondvalue is greater than the first value.
 19. The method of claim 18further comprising: applying a fourth voltage having a fourth value to afourth gate of a fourth memory cell of the device during the readoperation, the fourth memory cell coupled in series with the first,second, and third memory cells, wherein the fourth value is equal to thesecond value.
 20. The method of claim 18 further comprising: applyingthe first voltage having the first value to the second gate during anadditional read operation of the device; applying the third voltagehaving the third value to the first gate of during the additional readoperation; and applying the third voltage having the third value to thethird gate during the additional read operation.
 21. The method of claim20 further comprising: applying the second voltage having the secondvalue to a fourth gate of a fourth memory cell of the device during theadditional read operation.
 22. The method of claim 18, wherein the firstvalue is zero volts and the third value is approximately 600 milivoltsgreater than the second value.
 23. A method comprising: applying a firstvoltage having a first value to a first gate of a first memory cell of adevice during a read operation of the device; applying second voltagesto gates of second memory cells coupled in series with the first memorycell and located on a first side of the first memory cell, wherein atleast two of the second voltages have different values; and applyingthird voltages to gates of third memory cells coupled in series with thefirst memory cell and located on a second side opposite from the firstside of the first memory cell, wherein at least two of the thirdvoltages have different values.
 24. The method of claim 23, wherein oneof the second voltages includes a second value and one of the thirdvoltages includes a third value, and the second and third values areequal.
 25. The method of claim 24, wherein a first additional voltage ofthe second voltages includes a fourth value and a first additionalvoltage of the third voltages includes a fifth value, the fourth andfifth values are equal, and the fourth and third values are different.26. The method of claim 25, wherein a second additional voltage of thesecond voltages includes a sixth value and a second additional voltageof the third voltages includes a seventh value, the sixth and seventhvalues are equal, and the sixth and third values are different.